1. Field of the Invention
The present invention relates to a numerical control apparatus and a numerical control method for controlling a machine tool, and more particularly to a numerical control apparatus and a numerical control method for controlling a machine tool which machines prototypes or the like.
2. Background Art
Advances in the technology of numerically controlled machine tools have been so great that they can machine workpieces of complex shape at high speed with precision. At present, workpieces of complex shape cannot be machined without numerically controlled machine tools.
To generate machining programs, there are widely used interactive numerical control apparatus which comprise a numerical control apparatus with an interactive program generating function, and automatic programming apparatus for simply generating complex machining programs.
In the use of such numerical control apparatus, it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data for generating strict machining programs. The interactive numerical control apparatus and the automatic programming apparatus can be used to machine a number of workpieces.
For some machining processes for producing a prototype or a model, general-purpose milling machines, lathes, and the like are used which require a short period of time to carry out preparatory action such as attachment and detachment of workpieces, installation of tools, etc., and does not require machining programs to be generated. Machining on such machines or lathes has been carried out solely at the discretion of the operator.
Problems of general-purpose machine tools are that the number of available operators who can handle general-purpose machine tools is becoming smaller, and it is difficult for the general-purpose machine tools to carry out oblique linear machining, arcuate machining, or the like though they can effect linear machining without any problem.
If, on the other hand, a general numerically controlled machine tool is used to machine a prototype or a model, then it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data. While it is not impossible to define those data, the required programming process is too time-consuming and troublesome for machining a portion of a single workpiece.
To solve the above problems, the applicant has filed Japanese patent application No. 4-231836 on a numerical control apparatus which employs a general-purpose machine tool for carrying out simple machining processes to machine prototypes or the like.
Such a numerical control apparatus is widely used for machining a portion of a workpiece. Where a workpiece is to be machined into a relatively simple shape, the operator may want to machine the workpiece to its final shape. With the above numerical control apparatus, however, the operator himself is required to calculate all machining cycles and operate the tools, resulting in a time-consuming and tedious working process. Conversely, if a general numerical control apparatus is used, then since it is necessary to define machine coordinates, a machine origin, program coordinates, a machining origin, and other data, it is too time-consuming and tedious to machine only one workpiece on the general-purpose numerical control apparatus.
One frequent machining process performed when a prototype is to be produced by a machine tool is drilling. According to one drilling process, a workpiece is drilled at a group of points along a certain path on the workpiece. In such a drilling process, after a hole is formed at a certain point with a drilling machine, it is necessary to set and position the drill for a next hole. Accordingly, the drilling process has been complex, and it has been time-consuming to form holes at many points. The drill has not necessarily been positioned accurately as it has been positioned based on eye measurement. In view of the above background, there has been a demand for drilling a workpiece simply and accurately at a group of points thereon using the functions of a numerical control apparatus incorporated in a machine tool.
In the above numerical control apparatus, it has been customary to generate a designated shape based on the information which has been entered according to guidance information, and feed a tool along the designated shape by operating a manual pulse generator or the like when a workpiece is machined. The designated shape is only a portion, e.g., a linear portion or a corner portion, of an entire machining shape. Therefore, even when the workpiece is to be machined for the entire machining shape, it can only be machined from portion to portion in the entire machining shape, and cannot continuously be machined for the entire machining shape. Furthermore, when a plurality of workpieces are to be machined to the same shape, they have to be machined one by one because the entire machining shape for them is not recognized.